1. Field of the Invention
The present invention relates to a two-port valve for a vacuum operation, which is used for evacuating a vacuum chamber for chemical reaction in a physical or chemical machine or the like, for instance.
2. Description of the Prior Art
For instance, where a vacuum chamber for chemical reaction in a physical or chemical machine or the like is evacuated by a vacuum pump, when the gas in the chamber at a relatively high pressure (i.e., at or near the atmospheric pressure) is rapidly discharged, a turbulence of the gas occurs inside the vacuum chamber since a large volume of the gas flows all at once, stirring up particles adhered to an inner wall of the chamber and/or others, which may disturb an operation of processing. Further, the vacuum pump tends to suffer from an overload.
Therefore, there has been proposed a two-port valve which connects between a vacuum chamber and a vacuum pump, and comprises a main valve mechanism relatively widely openable and an auxiliary valve mechanism relatively narrowly openable, as disclosed in JP-A-8-166085, for instance. In an initial discharge phase, a fluid passage between the vacuum chamber and the vacuum pump is opened limitedly by the auxiliary valve mechanism to slowly discharge the gas in the vacuum chamber. When the inner pressure of the vacuum chamber is decreased to a sufficiently low level, the fluid passage is widely opened by the main valve mechanism to fully discharge the gas.
However, this conventional two-port valve having the two valve mechanisms, namely, the main and auxiliary valve mechanisms, is relatively complex in structure, and requires a lot of time and works to design and manufacture, and as well as a slightly higher manufacturing cost.